Slow log for performance analysis in Redis - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the command to view the slow log entries.

Redis

SLOWLOG [1]

Drag options to blanks, or click blank then click option'

AGET

BGETLOG

CGETSLOW

DGETSLOWLOG

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect subcommands like GETLOG or GETSLOW.

Confusing slow log commands with other Redis commands.

The correct command to view slow log entries is SLOWLOG GET.

2fill in blank

medium

Complete the command to reset the slow log entries.

Redis

SLOWLOG [1]

Drag options to blanks, or click blank then click option'

ARESET

BCLEAR

CRESETLOG

DRESETLOGS

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect subcommands like CLEAR or RESETLOGS.

Trying to delete slow logs with unrelated commands.

The command to reset the slow log entries is SLOWLOG RESET.

3fill in blank

hard

Fix the error in the command to get the last 5 slow log entries.

Redis

SLOWLOG GET [1]

Drag options to blanks, or click blank then click option'

Afive

B5

C'5'

Dlast5

Attempts:

3 left

💡 Hint

Common Mistakes

Using words like 'five' instead of the number 5.

Putting the number inside quotes which causes errors.

The correct way to specify the number of entries is with the integer 5, not a string or word.

4fill in blank

hard

Fill both blanks to retrieve slow log entries including ID and execution time.

Redis

SLOWLOG [1] [2]

Drag options to blanks, or click blank then click option'

AGET

BRESET

C10

DCLEAR

Attempts:

3 left

💡 Hint

Common Mistakes

Using RESET or CLEAR with a number, which is invalid.

Mixing subcommands and numbers incorrectly.

Use SLOWLOG GET 10 to retrieve the last 10 slow log entries.

5fill in blank

hard

Fill all three blanks to retrieve the last 3 slow log entries and then reset the log.

Redis

SLOWLOG [1] [2]; SLOWLOG [3]

Drag options to blanks, or click blank then click option'

ACLEAR

BGET

C3

DRESET

Attempts:

3 left

💡 Hint

Common Mistakes

Using CLEAR instead of RESET to reset the log.

Using strings instead of numbers for the count.

First, use SLOWLOG GET 3 to get the last 3 entries, then SLOWLOG RESET to reset the log.

Practice

1. What is the primary purpose of the Redis slow log?

easy

A. To clear the Redis cache automatically

B. To store all commands executed in Redis

C. To record commands that take longer than a set time to execute

D. To backup Redis data periodically

Solution

1. Step 1: Understand what slow log tracks

   The slow log records commands that exceed a certain execution time threshold.

2. Step 2: Differentiate from other Redis features

   It does not store all commands, clear cache, or backup data; it only logs slow commands.

3. Final Answer:

   To record commands that take longer than a set time to execute -> Option C

4. Quick Check:

   Slow log = records slow commands [OK]

Hint: Slow log tracks only slow commands, not all commands [OK]

Common Mistakes:

• Thinking slow log stores all commands
• Confusing slow log with cache clearing
• Assuming slow log is for backups

2. Which Redis command correctly retrieves the slow log entries?

easy

A. SLOWLOG LIST

B. SLOWLOG FETCH

C. SLOWLOG SHOW

D. SLOWLOG GET

Solution

1. Step 1: Recall the Redis slow log retrieval command

   The official command to get slow log entries is SLOWLOG GET.

2. Step 2: Verify other options

   Commands like SLOWLOG FETCH, SLOWLOG SHOW, and SLOWLOG LIST do not exist in Redis.

3. Final Answer:

   SLOWLOG GET -> Option D

4. Quick Check:

   Retrieve slow log = SLOWLOG GET [OK]

Hint: Use SLOWLOG GET to view slow log entries [OK]

Common Mistakes:

• Using non-existent commands like SLOWLOG FETCH
• Confusing with LIST or SHOW commands
• Misspelling the command

3. Given the following Redis commands executed in order:

SLOWLOG RESET
SLOWLOG LEN
SLOWLOG GET 2

What will be the output of SLOWLOG LEN immediately after the reset?

medium

A. 0

B. 2

C. An error message

D. The last 2 slow log entries

Solution

1. Step 1: Understand SLOWLOG RESET effect

   The SLOWLOG RESET command clears all slow log entries, so the log becomes empty.

2. Step 2: Check SLOWLOG LEN after reset

   Since the log is empty, SLOWLOG LEN returns 0, indicating no entries.

3. Final Answer:

   0 -> Option A

4. Quick Check:

   Reset clears log, length = 0 [OK]

Hint: Reset clears log; length after reset is zero [OK]

Common Mistakes:

• Expecting old entries after reset
• Confusing SLOWLOG LEN with SLOWLOG GET output
• Thinking reset causes error

4. You run SLOWLOG GET but receive an empty list even though you expect slow commands. What is the most likely cause?

medium

A. The slow log threshold is set too high, so no commands qualify

B. The Redis server is down

C. You need to restart Redis to enable slow log

D. The slow log is full and cannot record more entries

Solution

1. Step 1: Understand slow log threshold role

   Redis only logs commands slower than the configured threshold (default 10ms). If threshold is too high, no commands get logged.

2. Step 2: Eliminate other causes

   Redis server down would cause connection errors, not empty logs. Restart is not needed to enable slow log. Slow log size is limited but overwrites old entries, so it won't be empty due to fullness.

3. Final Answer:

   The slow log threshold is set too high, so no commands qualify -> Option A

4. Quick Check:

   High threshold = no slow commands logged [OK]

Hint: Check slow log threshold if no entries appear [OK]

Common Mistakes:

• Assuming Redis must restart to enable slow log
• Thinking slow log fills up and stops logging
• Confusing server down with empty slow log

5. You want to analyze slow commands that took longer than 50 milliseconds and keep only the last 5 entries. Which sequence of Redis commands achieves this?

hard

A. CONFIG SET slowlog-log-slower-than 50
SLOWLOG RESET
SLOWLOG GET 5

B. CONFIG SET slowlog-max-len 5
CONFIG SET slowlog-log-slower-than 50000
SLOWLOG RESET
SLOWLOG GET 5

C. CONFIG SET slowlog-log-slower-than 50000
SLOWLOG RESET
SLOWLOG GET 5

D. CONFIG SET slowlog-max-len 5
CONFIG SET slowlog-log-slower-than 50
SLOWLOG RESET
SLOWLOG GET 5

Solution

1. Step 1: Set threshold to 50 milliseconds

   Redis uses microseconds, so 50 ms = 50000 μs. Use CONFIG SET slowlog-log-slower-than 50000. A and C correct; B and D use 50 μs (too low).

2. Step 2: Limit slow log length to 5 entries

   Use CONFIG SET slowlog-max-len 5. Only A and D do this; B and C do not.

3. Step 3: Reset slow log and get last 5 entries

   SLOWLOG RESET clears old entries; SLOWLOG GET 5 retrieves last 5. All options include this.

4. Step 4: Choose correct option

   Only A sets both max-len to 5 and threshold to 50000 μs (50 ms).

5. Final Answer:

   CONFIG SET slowlog-max-len 5 CONFIG SET slowlog-log-slower-than 50000 SLOWLOG RESET SLOWLOG GET 5 -> Option B

6. Quick Check:

   Threshold 50ms = 50000μs, max len 5, reset, get 5 [OK]

Hint: Set threshold in microseconds and max length before reset [OK]

Common Mistakes:

• Confusing milliseconds with microseconds in threshold
• Not setting max length to limit entries
• Forgetting to reset slow log before analysis